Air-Stable Benzimidazoline n-Type Dopants for Conductive Host Materials with Low Electron Affinities

Nowadays a growing interest is devoted to molecular reductants for solution-processable organic semiconductors such as organic light-emitting diodes (OLEDs), organic photovoltaics (OPVs), thermoelectric generators (TEGs), organic field-effect transistors (OFETs), and circuitry in which they can increase the conductivity, reduce bulk ohmic losses and/or decrease carrier-injection barriers.[1] They can also modulate the work function (WF) of inorganic electrode materials and push the performance of inverted perovskite solar cell by boosting the conductivity of PCBM type ETMs. However, the availability of high-performance and airstable solution-processable n-doped materials remains limited, primarily due to the low electron affinity of n-type materials that strongly restricts the n-doping level. Benzimidazoline-based reductants (Figure1) have recently emerged as efficient and air-stable n-type dopants in electron transporting materials (ETMs) to increase electrical conductivities.[2] Hence we designed and synthesized a series of Benzimidazoline based compounds as air-stable n-dopants and their doping abilities have been surveyed by analysing the electron conductivity trend of organic semiconductors. Moreover an in-depth study of their electrochemical characteristics have been carried out and their molecular orbital energy levels investigated. The most efficient n-doping molecules are intended to largescale, printed electronics for energy-harvesting and storage applications

Efficient sunlight harvesting by A4 b-pyrrolic substituted ZnII porphyrins : a mini-review

Dye-Sensitized Solar Cells (DSSCs) are a highly promising alternative to conventional photovoltaic silicon-based devices, due to the potential low cost and the interesting conversion efficiencies. A key-role is played by the dye, and porphyrin sensitizers have drawn great interest because of their excellent light harvesting properties mimicking photosynthesis. Indeed, porphyrins are characterized by strong electronic absorption bands in the visible region up to the near infrared and by long-lived \u3c0* singlet excited states. Moreover, the presence of four meso and eight \u3b2-pyrrolic positions allows a fine tuning of their photoelectrochemical properties through structural modification. Trans-A2BC push-pull ZnII porphyrins, characterized by a strong and directional electron excitation process along the push-pull system, have been extensively investigated. On the other hand, A4 \u3b2-pyrrolic substituted tetraaryl ZnII porphyrins, which incorporate a tetraaryl porphyrinic core as a starting material, have received lower attention, even if they are synthetically more attractive and show several advantages such as a more sterically hindered architecture and enhanced solubility in most common organic solvents. The present contribution intends to review the most prominent A4 \u3b2-substituted ZnII porphyrins reported in the literature so far for application in DSSCs, focusing on the strategies employed to enhance the light harvesting capability of the dye and on a comparison with meso-substituted analogs

Second Order Nonlinear Optical Properties of 4-Styrylpyridines Axially Coordinated to A4 ZnII Porphyrins: A Comparative Experimental and Theoretical Investigation

In this research, two 4-styrylpyridines carrying an acceptor \u2013NO2 (L1) or a donor \u2013NMe2 group (L2) were axially coordinated to A4 ZnII porphyrins displaying in 5,10,15,20 meso position aryl moieties with remarkable electron withdrawing properties (pentafluorophenyl (TFP)), and with moderate to strong electron donor properties (phenyl (TPP) < 3,5-di-tert-butylphenyl (TBP) < bis(4-tert-butylphenyl)aniline) (TNP)). The second order nonlinear optical (NLO) properties of the resulting complexes were measured in CHCl3 solution by the Electric-Field-Induced Second Harmonic generation technique, and the quadratic hyperpolarizabilities \u3b2\u3bb were compared to the Density Functional Theory (DFT)-calculated scalar quantities \u3b2||. Our combined experimental and theoretical approach shows that different interactions are involved in the NLO response of L1- and L2-substituted A4 ZnII porphyrins, suggesting a role of backdonation-type mechanisms in the determination of the negative sign of Electric-Field-Induced Second Harmonic generation (EFISH) \u3b2\u3bb, and a not negligible third order contribution for L1-carrying complexes

Going beyond the Surface: a Glance inside Smart Conducting Molecular Surfaces through a Multitechnique Approach

Conducting organic polymers, COPs, are smart materials that merge some of the most interesting properties of common polymers (e.g. flexibility, processability, etc.) with high electrical conductivity of metals. Research in this field is currently attracting increasing attention, since these innovative materials are very promising for a great variety of applications, from energetics to electronics and sensoristics, even from an industrial point of view. Chirality makes COPs even smarter materials, opening the way to enantioselective electroanalysis/electrosynthesis. In particular the \u201cinherent chirality\u201d concept proposed by our groups some years ago actually represented a breakthrough, significantly improving all other literature approaches so far proposed, making possible deposition of conducting homochiral oligomeric films acting as effective, efficient and robust enantioselectors toward a great variety of chiral analytes, in different media.. The further natural step is the comprehension of the actual working mechanism of these intelligent surfaces. To reach such intriguing target a deep and multivariate characterization is mandatory, to reveal as much properties as possible that could be finally combined to depict a complete portrait of these conducting inherently chiral films. In this short presentation we will glance at these smart chiral conducting molecular surfaces, following an ideal tour from outside (i.e. surface appearance) to their inner parts (i.e. optical and electronic features). The support of Fondazione Cariplo/Regione Lombardia (Project 2016-0923) and SmartMatLab are gratefully acknowledged

4D-π-1A Type β-Substituted ZnII-Porphyrins : Ideal Green Sensitizers for Building-Integrated Photovoltaics [4D-pi-1A type beta-substituted Zn-II-porphyrins: ideal green sensitizers for building-integrated photovoltaics]

Two novel green \u3b2-substituted ZnII-porphyrins, G1 and G2, based on a 4D-\u3c0-1A type substitution pattern have been synthesized. Their enhanced push-pull character, by reduction of H-L energy gaps, promotes broadening and red-shifting of absorption bands. The effective synthetic pathway and the remarkable spectroscopic properties make G2 ideal for BIPV application

Electronic properties of electron-deficient Zn(II) porphyrins for HBr splitting

Two different high potential Zn(II) porphyrin designs carrying either 4 or 5 meso pentafluorophenyl moieties as electron acceptor groups and a further electron withdrawing branch inserted in either the \u3b2 (1) or meso (2) position were tested in photoelectrosynthetic cells for HBr splitting. Photoaction spectra in the presence of HBr showed that red photons up to 700 nm could be harvested and converted and that 2 performed better than 1, thanks to better electronic properties of the excited state, favored by the insertion of the benzothiadiazole electron withdrawing group. Photoanodic performances in the presence of HBr, however, remained low, due to inefficient regeneration of the oxidized sensitizer as a result of an insufficient driving force for Br- oxidation

Thiahelicene-based inherently chiral films for enantioselective electroanalysis

Chiral electroanalysis could be regarded as the highest recognition degree in electrochemical sensing, implying the ability to discriminate between specular images of an electroactive molecule, particularly in terms of significant peak potential difference. A groundbreaking strategy was recently proposed, based on the use of \u201cinherently chiral\u201d molecular selectors, with chirality and key functional properties originating from the same structural element. Large differences in peak potentials have been observed for the enantiomers of different chiral molecules, also of applicative interest, using different selectors, all of them based on atropisomeric biheteroaromatic scaffolds of axial stereogenicity. However, helicene systems also provide inherently chiral building blocks with attractive features. In this paper the enantiodiscrimination performances of enantiopure inherently chiral films obtained by electrooxidation of a thiahelicene monomer with helicoidal stereogenicity are presented for the first time. The outstanding potentialities of this novel approach are evaluated towards chiral probes with different chemical nature and bulkiness, in comparison with a representative case of the so far exploited class of inherently chiral selectors with axial stereogenicity. It is also verified that the high enantiodiscrimination ability holds as well for electron spins, as for atropisomeric selectors

Influence of alkoxy chains envelope on the interfacial photoinduced processes in tetraarylporphyrin-sensitized solar cells

The introduction of alkoxy chains in the molecular architecture of meso push-pull porphyrins is of paramount importance aiming at high performing dye-sensitized solar cells (DSSCs) based on these specific sensitizers. Recently, we have demonstrated that the same approach is fruitful even if it is applied to tetraarylporphyrins with an acceptor/anchoring substituent in the \u3b2-pyrrolic position. In particular, among the ortho-ortho, the ortho-para and the ortho-functionalization of the aryl rings with an octyloxy chain, we identified the latter as the most performing in the series, showing a good balance between the dye loading and the reduction of \u3c0-\u3c0 aggregation. Herein, focusing our attention on the mono-ortho-functionalized molecular structure, we have investigated the effect of the alkoxy chain length and nature on the reduction of dye-to-dye aggregation as well as on the enhancement of light harvesting capabilities, finding an almost linear relationship between the device photon conversion efficiency (PCE) and the alkoxy chain length both in the presence and in the absence of a co-disaggregating agent